One-To-Many-Collections with joined-sublcass

MadEagle · **Joined:** Thu Feb 05, 2004 6:04 am **Posts:** 5

Hi all,

I have the following problem:

I have a class called Project that has a collection (set) called financeRealTransactions in a one-to-many relation. The referenced class ist FinanceReal and is a joined-subclass of AbstractTransaction. The problem seems to be the the key column that is used in the collection is part of AbstractTransaction and not FinanceReal. Every time I try to access the collection Hibernate throws a "net.sf.hibernate.JDBCException: could not initialize collection". If I run the Schema{Export|Update} tool it tries to create a column "project" to the financereal table. I expected Hibernate to realise that the key column is part of the parent class (AbstractTransaction) and not the child class (FinanceReal).

Am I doing something wrong here? Is there a way to tell Hibernate to look into the AbstractTransaction table? Is this a bug? Or a missing feature? Or am I just thinking into the wrong direction here?

I am using Hibernate 2.1.2. The relevant part of my mapping document follows:

Code:

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC 
   "-//Hibernate/Hibernate Mapping DTD//EN" 
   "http://hibernate.sourceforge.net/hibernate-mapping-2.0.dtd">

<hibernate-mapping>
   <class name="persistence.PersistentObject" table="PERSISTENTOBJECT">
      <id name="id" type="long" unsaved-value="-1">
         <generator class="native"/>
      </id>
      <version column="version" name="version" type="timestamp"/>

      <joined-subclass name="co_objects.Project" table="project">
         <key column="id"/>

         <property name="name" type="string" length="100" not-null="true"/>
         <set name="financeRealTransactions">
            <key column="project"/>
            <one-to-many class="transactions.FinanceReal"/>
         </set>
      </joined-subclass>
      
      <joined-subclass name="transactions.AbstractTransaction" table="abstract_trans">
         <key column="id"/>
         <property name="relevantPointInTime" type="date" not-null="true"/>
         <many-to-one name="project" class="co_objects.Project" not-null="true"/>
         <joined-subclass name="transactions.FinanceReal" table="finance_real">
            <key column="id"/>
            <property name="invoiceDate" type="date"/>
            <property name="invoiceReference" type="string" length="50"/>
         </joined-subclass>
      </joined-subclass>
   </class>
</hibernate-mapping>

Thanks for any help, MadEagle

gavin · **Posted:** Fri Feb 06, 2004 4:53 am

I dunno, seems to me that Hibernate s being quite sane here...

Change to:

Code:

<set name="financeRealTransactions">
        <key column="project"/>
        <one-to-many class="transactions.AbstractTransaction"/>
</set> 

If the association is really to the superclass table.

MadEagle · **Joined:** Thu Feb 05, 2004 6:04 am **Posts:** 5

OK, that would solve the problem but AbstractTransaction has more than one subclass (I ommitted the others to keep the mapping document readable) so this set would then give me all AbstractTransactions and not only FinanceReals, right? I have to admit I didn't test this. Is my assupmtion correct?

Thanks for your answer, MadEagle

emmanuel · **Posted:** Fri Feb 06, 2004 7:59 am

MadEagle · **Joined:** Thu Feb 05, 2004 6:04 am **Posts:** 5

Hm, is there any reason why Hibernate behaves that way? From my (pretty uninformed an inexperienced) point of view I would have expected "object oriented" behaviour rather than "table oriented".

MadEagle

emmanuel · **Posted:** Fri Feb 06, 2004 9:37 am

I don't follow you.
You told Hibernate that AbstractTransaction has a many-to-one with project, this is fine then to set the FK in the AbstractTransaction and not in financial.

l.masini · **Posted:** Fri Feb 06, 2004 9:56 am

I overused OO ineritance in Hibernate, against all I read here, and it works GREAT.
I had your same problem, and I solved it this way:

this way the mapping create a column in the Set class that actually is used only by the relationship.
Ciao.

MadEagle · **Joined:** Thu Feb 05, 2004 6:04 am **Posts:** 5

emmanuel wrote:

You told Hibernate that AbstractTransaction has a many-to-one with project, this is fine then to set the FK in the AbstractTransaction and not in financial.

AbstractTransaction is not one of the classes that I want to use in my business logic, but FinanceReal that extends it is. There is a bunch of classes that extend AbstractTransaction. They all need the many-to-one with project but they all have different attributes that extend AbstractTransaction. Therefore the many-to-one is in AbstractTransaction but if for example I try to get all FinanceReal objects for a project Hibernate tries to look into the FinanceReal table instead of AbstractTransaction.

To model the classes in a way that Hibernate would support would mean to put in every child class of AbstractTransaction the project property which defeats the principles of object oriented programming, right?

MadEagle

MadEagle · **Joined:** Thu Feb 05, 2004 6:04 am **Posts:** 5

l.masini wrote:

I overused OO ineritance in Hibernate, against all I read here, and it works GREAT.
I had your same problem, and I solved it this way:

this way the mapping create a column in the Set class that actually is used only by the relationship.

Hm, interesting idea, will try that out and see if it solves my problem. Thanks.

MadEagle